AbstractThe Permian Coconino Sandstone at Grand Canyon National Park has yielded an important vertebrate ichnofauna.
Currently all specimens from the Coconino Sandstone are assigned to species of
Chelichnus. A morphologically distinct trackway has been discovered along the Hermit Trail and in Marble Canyon that differs from
Chelichnus in: (1) possession of tail drag; (2) disparity in size between manus and pes impressions; (3) pace angulation greater than
90o; and (4) L-shaped manus impression. This represents a previously unrecognized morphology for Permian eolianites.

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INTRODUCTION

Figure 1. Cross section view of the Permian stratigraphy near the Hermit
Trail at Grand Canyon National Park. The Coconino Sandstone is overlain
by the Kaibaba Limestone.

Paleozoic tetrapod ichnofaunas from Grand Canyon National Park are
among the most significant in North America (Hunt and Santucci, 1998a). The
majority of specimens were collected by Charles Gilmore of the United States
National Museum (Smithsonian) and described by him in a series of classic works
(Gilmore, 1926b, 1927b, 1928a). Santucci and Wall (1995) conducted a preliminary
reconnaissance of the Coconino Sandstone in the area of the Hermit Trail in
Grand Canyon National Park (Fig. 1). The purpose of this paper is to describe
an unusual track morphology from that location that is distinct from those previously
reported within the Coconino Sandstone.

PALEOZOIC TETRAPOD TRACKS FROM THE GRAND CANYON

Schuchert (1918) is credited as the first collector of tetrapod tracks in Paleozoic
strata on the South Rim of the Grand Canyon. Lull (1918) utilized the portion
of the collection from the Permian Coconino Sandstone to publish the first scientific
description of Paleozoic tetrapod tracks from Arizona. In 1924, the National
Park Service invited Charles Gilmore to visit Schuchert's locality and to prepare
an in situ exhibit on a now abandoned portion of the Hermit Trail (Spamer,
1984). Gilmore (1926b) described this new collection of Coconino ichnofossils
and was later funded, by the Marsh Fund Committee of the National Academy of
Sciences (1926) and the Grand Canyon Exhibit Committee of the National Academy
of Sciences (1927), to make additional collections and exhibits (Spamer, 1984).
In addition to the new trace fossil collections from the Coconino, Gilmore collected
vertebrate tracks from the Hermit Shale (Permian) and Wescogame Formation of
the Supai Group (Pennsylvanian). Gilmore described this new material in additional
monographs (Gilmore, 1927b, 1928a) and a short paper on the first tracks from
the North Rim (Gilmore and Sturdevant, 1928). Gilmore also wrote three more
popular papers describing his collecting efforts in the Grand Canyon (Gilmore,
1926a, 1927a, 1928b).

For the next 70 years there was little reevaluation of Gilmore's work except
by Don Baird of Princeton (Baird, 1952, Baird in Spamer, 1984). A renaissance
in Paleozoic track studies took place during the mid-1990's. The Rosetta Stone
for a new re-evalualtion of Permian tracks was provided by studies of the extensive
ichnofaunas from the redbeds of southern New Mexico (Haubold et al., 1995a,
b; Hunt et al., 1995). The New Mexico tracksites provided large sample sizes
of all the most significant Permian ichnotaxa and included a broad range of
preservational variants. These samples provided a new perspective on the plethora
of ichnotaxonomic names of tetrapod tracks from Permian redbeds, most of which
had been described on the basis of small sample sizes. During the same timeframe
there was a major reevaluation of the equally confused ichnotaxonomy of tetrapod
tracks from Permian eolianites (Morales and Haubold, 1995; Haubold et al., 1995a,
b; McKeever and Haubold, 1996; Haubold, 1996; Hunt and Santucci, 1998a,b). Hunt
and Santucci (1998a) presented a reassessment of the ichnotaxonomy of the Coconino
tracks from Grand Canyon National Park on the basis of this new synthesis (Table
1).

TETRAPOD ICHNOLOGY OF THE COCONINO SANDSTONE

The first fossil footprints to be described in the scientific literature came
from Permian eolianites of Scotland (Grierson, 1828). Subsequently, paleontologists
described important ichnofaunas from eolian strata of Germany (Cornberger Sandstein),
Colorado (Lyons Sandstone), and Arizona (Coconino Sandstone, DeChelly Sandstone),
as well as additional specimens from Scotland (Hopeman, Corncockle and Locharbriggs
Sandstone formations). An extensive literature describes many ichnotaxa from
these formations. However, recent work spearheaded by Hartmut Haubold has demonstrated
that virtually all tetrapod tracks from Permian eolianites represent three ichnospecies
of one ichnogenus, with only the rarest exceptions (Haubold et al., 1995b; McKeever
and Haubold, 1996; Haubold, 1996). All of the Coconino vertebrate tracks apparently
fall within three species of Chelichnus (McKeever and Haubold, 1996).
Chelichnus is characterized by rounded manual and pedal impressions
that are of nearly equal size and that exhibit five short, rounded toe impressions
(though fewer than five may be preserved). Trackways have a pace angulation
of about 90o, and the manual and pedal impressions are close together
(McKeever and Haubold, 1996). The three valid species of Chelichnus are
distinguished on the basis of size alone and are presumed to be the tracks of
a caseid-like animal (Haubold, 1971). Chelichnus bucklandi has pedal
impression lengths of 10-25 mm, C. duncani of 25-75 mm and C. gigas
of 75-125 mm (McKeever and Haubold, 1996). Thus, all of Gilmore's and Lull's
named ichnotaxa from the Coconino Sandstone of the Grand Canyon can be placed
in one of these three species. Gilmore (1927b) was aware of the similarity between
some of his specimens from the Grand Canyon and those from Scotland, but he
persisted with his (and Lull's) distinct ichnotaxonomy (Gilmore, 1928a).

Singularly, size is not the ideal criterion with which to distinguish between
ichnospecies, however, the revised ichnotaxonomy presented here represents the
current consensus (Table 1). The low ichnotaxonomic diversity of the Coconino
is in keeping with the low animal diversity that would be expected in an arid
dunefield.

Gilmore was aware that the Coconino Sandstone
and Hermit Shale were deposited in different sedimentary
environments, however, Baird (1965) was the first to
emphasize that the differences between the Permian ichnofaunas of
the redbeds of the American West and those of eolianites
might be a result of facies differences. There has been a long
tradition of recognizing ichnofacies in invertebrate traces, but
the concept has only recently been applied to vertebrate
tracks (Lockley et al., 1994). Tetrapod ichnofacies have been
defined as "multiple ichnocoenoses that are similar
in ichnotaxonomic composition and show recurrent
association in particular environments (Lockley et al., 1994, p. 242).
Lockley and others (1994), Hunt and others (1995),
Haubold (1996) and Hunt and Lucas (1998a) have all discussed
Permian tetrapod ichnofacies.

The low-diversity tetrapod ichnofauna of the Coconino Sandstone has been interpreted
to represent the Chelichnus ichnofacies (= Laoporus ichnofacies
of Lockley et al., 1994) that is known from the DeChelly and Coconino sandstones
of Arizona, the Lyons Sandstone of Colorado, the Hopeman, Corncockle and Locharbriggs
Sandstone formations of Scotland, the Cornberger Sandstein of Germany and the
Los Reyunos Formation of Argentina (Hunt and Lucas, 1998a, b; Hunt and Santucci,
1998a).

Figure 3. Overview of tracksite looking up the dune face. A small Chelichnus
duncani trackway (left arrows) zigzags up the dune face to the right
ofo the large enigmatic trackway (right arrows).

In 1993, we noted a morphologically enigmatic trackway near the present Hermit
Trail and have subsequently reexamined this trackway and others in the same
area. The trackway is distinct from most Coconino Chelichnus tracks in
five characteristics (Fig. 2 and 3): (1) the trackway proceeds directly up the
dune face, whereas most trackways traverse at an oblique angle; (2) the tracks
are much larger than average for the Coconino; (3) there is a prominent, sinuous
tail drag; (4) the manus print is smaller than the pes: and, (5) the manus track
is L-shaped. Subsequently, a second trackway of similar morphology was discovered
near the first trackway. We later noted that Price (1998, p. 21) illustrated
a similar trackway from the Coconino near Buck Farm Canyon, a side canyon of
Marble Canyon within Grand Canyon National Park. Price's (1998, p. 21) specimen
also has a sinuous tail-drag and L-shaped manus tracks (note first manus print
on the left side of trackway in foreground of photograph).

The first Hermit Trail trackway is preserved in situ on a bedding plane
that dips 55°. The left portion of the trackway is more distinct than the
right. The pes tracks are ovoid with no distinct digital impressions. The tracks
are oriented with the long axis in the direction of travel. The pes tracks average
10 cm in length and exhibit a stride between 55 and 58 cm. The manus tracks
average 8 cm in antero-posterior length. These tracks are variable in morphology.
Several are L-shaped with one axis directed antero-lateral to the direction
of travel and the other lateral to slightly postero-lateral. The tail drag is
continuous and sinuous, however, it is variable in width with a maximum of 5
cm. The pace angulation varies from between 90° to 120°.

These trackways do not conform to any of the trackway morphologies described
by Gilmore. Furthermore, they differ from Chelichnus (sensu McKeever
and Haubold, 1995) in: (1) possession of tail drag; (2) disparity in size between
manus and pes impressions; (3) pace angulation greater than 90°; and (4)
L-shaped manus impression. The only other tracktypes identified in Permian eolianites
are lacertoid in morphology (Haubold et al., 1995). These tracks do have larger
pace angulations, disparity in size between manus and pes impressions, and tail
drag marks. However, lacertoid tracks are smaller and possess small sole pads.

In conclusion, the new trackway appears to represent a new component of the
Coconino ichnofauna. Further study is needed to confirm whether this represents
a new ichnotaxon. It is highly unlikely, but still possible that this track
morphology represents an extreme extramorphological variant of Chelichnus.

ACKOWLEDGEMENTS

We thank Terrell Jones, Masaki Matsukawa, Luke Santucci and Bill Wall for assistance
with fieldwork. We also extend our appreciation to John Foster, Spencer Lucas,
Lindsay McClelland, and Deb Mickelson for reviewing the draft version of this
manuscript.

Santucci, V.L. and W.P. Wall, 1995. Climbing up sand dunes in the Permian:
New tracksites from Grand Canyon National Park, Arizona. in Santucci,
V. L. and McClelland, L., (eds.), National Park Service Paleontological Research:
United States Department of the Interior, National Park Service, Technical Report
NPS/NRPO/NRTR-95/16, p. 64-65.

Schuchert, C., 1918. On the Carboniferous of the
Grand Canyon of Arizona: American Journal of Science,
fourth series, v. 45, p. 362-369.

Spamer, E. E., 1984. Paleontology in the Grand Canyon
of Arizona: 125 years of lessons and enigmas from the
late Precambrian to the present: The Mosasaur, v. 2, p.
45-128.